path/query params lists exclude null from json ser

[l-trotta]

Fixes #1218

[github-actions]

The backport to 9.4 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-9.4 9.4
# Navigate to the new working tree
cd .worktrees/backport-9.4
# Create a new branch
git switch --create backport-1222-to-9.4
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 a4b9efbd16ecd57a85e42c2669fd8f710249ae43
# Push it to GitHub
git push --set-upstream origin backport-1222-to-9.4
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-9.4

Then, create a pull request where the base branch is 9.4 and the compare/head branch is backport-1222-to-9.4.